A. Field of the Invention
The present invention relates to tie rods of the type used to reinforce ventilating ducts which convey air for heating, ventilating or air conditioning (HVAC) the interior spaces of buildings or similar structures. Such tie rods are used to prevent excessive flexure of duct walls in response to fluctuations of air pressure exerted on walls of the duct. More particularly, the invention relates to a method and apparatus for manufacturing self-sealing reinforcement tie rods for ventilating ducts.
B. Description of Background Art
Ductwork used to heat, ventilate, or air condition buildings usually consists of elongated lengths of tubing comprising individual duct sections which are coupled together to form a continuous, air-tight duct for conveying flowing air. Typical duct tubing is made of a material such as sheet metal which is relatively strong but sufficiently light in weight to minimize the size and weight of fasteners and structural components required to support the ductwork, as well as maintaining materials and fabrication costs of the ductwork itself at reasonable levels. Thus, typical ducts are made of relatively thin sheet steel ranging in thickness from 26 gauge (0.0188 inch thick) to 16 gauge (0.0625 inch thick).
Sheet metal ducts have rectangular, circular or oval cross section shapes, and are often manufactured and supplied in pre-cut lengths or sections with transversely outwardly protruding interconnection flanges provided at opposite longitudinal ends of the section, to facilitate interconnecting duct sections at a job site and thus forming air conveying ducts of desired lengths and orientations.
Ducts of the type described above are available in a wide variety of sizes, having cross-section dimensions which range from a few inches to several feet. Moreover, a wide range of width-to-height or aspect ratios of rectangular ducts are available. For example, a typical 18 inch high duct may have a width in the range of 2 feet to 4 feet, and a length of 5 feet.
Whatever the shape, size and aspect ratio of the duct, the relatively small thickness of its walls relative to its cross-sectional dimensions results in the duct walls being relatively flexible. Thus, conventional ducts may experience relatively large, possibly destructive deformations if static or dynamic differential air pressure between the interior and exterior of the duct exceeds pre-determined threshold values. For this reason, mechanical engineering standards as well as applicable building codes require that duct work used to conduct air in certain heating, ventilating, and air conditioning (HVAC) applications be reinforced against expansion when positively pressurized and/or against collapse when negatively pressurized.
A widely employed reinforcement method that meets code requirements consist of installing elongated straight, rigid reinforcement members within a duct at pre-determined spacings which depend upon the rigidity of the duct, and upon the maximum differential pressures which it may encounter. Such reinforcement members are disposed perpendicularly between inner surfaces of opposite walls of the duct and fastened at opposite ends thereof to those walls. One such approved reinforcement member which is in current use consists of a threaded steel tie rod which has installed onto each end thereof a first, inner nut which is threadingly advanced to a predetermined distance inward from the end of the rod. The distance between the outer faces of the inner nuts is made equal to the minimum cross-sectional dimension, i.e., the height of the duct. The tie rod is positioned within a duct perpendicularly between a pair of opposed walls of the duct, and opposite ends of the threaded rod are each inserted through a separate one of a pair of transversely or vertically aligned holes provided through the duct walls. A pair of external nuts are then threaded onto the opposite ends of the threaded rod which protrude outwardly through the duct wall holes. Each external nut is then tightened onto the threaded rod against the outer surface of the duct wall, while the adjacent inner nut is held against rotation with a separate wrench. For large ducts, this operation requires two workmen.
Another prior-art duct reinforcement uses an elongated tube containing in opposite ends of the bore openings thereof an internally threaded fastener member which is fixed in the tube and which is adapted to receive a machine screw inserted through a duct wall hole. This reinforcement method also sometimes requires that the tube being gripped while the external machine screw is torqued, which again may require two workmen.
A third type of prior art tie rod used to reinforce HVAC ducts, which is a variation of the first method, uses a tube which encloses a threaded rod, the latter being secured between the walls of the duct by two external nuts, and is no easier to install than the other two types described above.
In addition to being somewhat difficult and time consuming to install, in accordance with certain code requirements, prior art reinforcement tie rods of the type discussed above must make an air-tight seal with the duct wall holes through which they protrude, thus requiring installation of a resilient sealing element such as a gasket or washer between the exterior nut or screw head and the duct wall. If the exterior nut or screw is torqued too tightly, such resilient elements can be deformed or damaged, and may ultimately fail to achieve sealing.
Motivated by limitations of prior art rod fasteners of the type discussed above, the present inventor developed a self-sealing reinforcement tie rod for reinforcing ventilating ducts. That tie rod was disclosed in U.S. patent application Ser. No. 09/307,270, filed May 7, 1999, now U.S. Pat. No. 6,116,833, issued Sep. 12, 2000. The novel reinforcement tie rod disclosed in the foregoing reference includes a length of threaded steel rod which is slightly longer, e.g., about 1-xc2xc inches, than the height of ducts which the tie rod is intended to reinforce. Thus, for use in 12-inch high ducts, the threaded rod portion of the tie rod according to the previous invention may have a typical diameter of about xe2x85x9c-inch and a length of about 13-xc2xc inches. The tie rod according to the prior invention also includes a pair of abutment structures fastened to opposite end portions of the threaded rod, inwards of the outer transverse end walls of the rod. Each abutment structure includes a longitudinally inwardly located tubular part which receives the threaded rod, and is permanently fastened thereto by, for example, crimping the wall of the tubular section into the threads of the rod. Each abutment structure also includes a longitudinally outwardly located annular flange which is disposed transversely to the axis of the threaded rod. The longitudinal spacing between the outer transverse walls of the abutment structure flanges is made nearly equal to the height of the duct. Thus, when the rod is placed inside a duct and opposite ends of the rod are inserted outwardly through a pair of vertically aligned holes made in the upper and lower walls of the duct, the outer transverse surfaces of the two abutment structure flanges abut the opposed inner duct wall surfaces, and each end of the rod protrudes about ⅝-inch outwardly from the adjacent duct wall.
According to the prior invention, the outer longitudinal portion of the bore in the tubular part of each abutment structure flares arcuately outwardly to join the outer transverse flange wall of the abutment structure, forming an annular cavity between the flange wall surface and threaded rod. The cavity has a diameter which tapers smoothly radially and longitudinally outwardly towards the flange. Prior to installation of the tie rod in a duct, a pair of resilient O-rings having an inner diameter slightly less than that of the threaded rod are slipped onto opposite outer ends of the rod.
The tie rod according to the prior invention also includes a pair of internally threaded fasteners located externally to the duct, which are threaded onto opposite ends of the threaded rod which protrude outwardly through the duct walls. In the preferred embodiment, each external threaded fastener consists of a flare nut having an outer hexagonal head and an inner annular skirt flange which flares outwardly from the head, the skirt having a flat lower or inner surface. When the flare nut is threaded down onto the protruding length of the threaded rod, and tightened down onto the outer surface of a duct wall, the O-ring is compressed between the inner surface of the duct wall and the outer transverse wall of an abutment structure flange. Further tightening of the flange nut on the threaded rod causes the O-ring to cold flow partially into the arcuately curved annular cavity between the flange wall and rod, and against the outer cylindrical wall surface of the threaded rod, thus forming a highly effective hermetic seal of the hole through the duct wall.
The present invention provides an efficient method and apparatus for manufacturing self-sealing reinforcement tie rods of the type described above.
An object of the present invention is to provide a method for manufacturing self-sealing reinforcement tie rods for reinforcing HVAC ducts, in which flanged abutment structures for abutting opposed walls of a duct are permanently secured onto opposite ends of a threaded tie rod.
Another object of the invention is to provide a method for crimping a tubular abutment structure onto a threaded tie rod.
Another object of the invention is to provide a method for permanently crimping the tubular crown of a flanged abutment structure onto a threaded rod, by crimping the outer wall surface of the crown with sufficient radially inwardly directed force to permanently indent the threaded rod and force cold flow of a portion of the inner wall surface of the crown into the indentation.
Another object of the invention is to provide a method for manufacturing self-sealing reinforcement tie rods in which a threaded tie rod is inserted through the inner bore of the tubular crown portion of a flanged abutment structure to a predetermined extension distance outward of the outer, flanged portion of the abutment structure, and a plurality of crimps are made externally into the outer longitudinal wall surface of the crown with sufficient force to indent the longitudinal wall surface of the threaded rod and force a portion of the inner longitudinal wall surface material of the crown to cold-flow into permanent locking engagement within the indentation in the threaded rod.
Another object of the invention is to provide a method for manufacturing a self-sealing reinforcement tie rod in which the outer flanged portion of a flanged abutment structure is positioned on a work surface, a threaded tie rod is inserted into the bore of the abutment structure to a predetermined extension distance beyond the outer surface of the flange portion and below the work surface, and radially inwardly directed crimping forces applied to the external longitudinal wall surface of the crown portion of the abutment structure, of sufficient magnitude to permanently deform the longitudinal wall surface of the threaded rod and cause cold flow of the inner wall surface of the crown portion into permanent locking engagement within indentations in the threaded rod.
Another object of the invention is to provide a method for manufacturing a self-sealing reinforcement tie rod in which an O-ring is positioned on a work surface, the flange portion of a tubular abutment structure is positioned coaxially over the O-ring, a threaded tie rod is inserted into the bore of the crown portion of the abutment structure a predetermined extension distance outward of outer transverse wall surface of the flange and the O-ring, and radially inwardly directed crimping forces applied to the outer longitudinal wall surface of the crown surface of the abutment structure, of sufficient magnitude to permanently indent the longitudinal wall surface of the threaded rod and induce cold flow of radially overlying portions of the inner wall surface of the crown into permanent locking engagement within the indentations.
Another object of the invention is to provide an apparatus for manufacturing self-sealing reinforcement tie rods for HVAC ducts which includes a work table having in the surface thereof an indentation for receiving the outer flange portion of a tubular abutment structure, two pairs of diametrically opposed punches longitudinally spaced circumferentially apart at ninety degree intervals, and actuator means for forcing the punches radially inwardly against the outer longitudinal wall surface of the upper crown portion of the abutment structure with sufficient force to permanently indent the outer longitudinal wall surface of a threaded tie rod inserted into the bore of the abutment structure, and cause cold-flow of a portion of the inner longitudinal wall surface of the crown into the indentations.
Various other objects and advantages of the present invention, and its most novel features, will become apparent to those skilled in the art by perusing the accompanying specification, drawings and claims.
It is to be understood that although the invention disclosed herein is fully capable of achieving the objects and providing the advantages described, the characteristics of the invention described herein are merely illustrative of the preferred embodiments. Accordingly, I do not intend that the scope of my exclusive rights and privileges in the invention be limited to details of the embodiments described. I do intend that equivalents, adaptations and modifications of the invention reasonably inferable from the description contained herein be included within the scope of the invention as defined by the appended claims.
Briefly stated, the present invention comprehends a method and apparatus for manufacturing self-sealing reinforcement tie rods of the type used to reinforce ventilating ducts which convey air for heating, ventilating or air conditioning (HVAC). This type of tie rod includes an elongated threaded rod having a pair of abutment structures adapted to brace opposite walls of a duct. The abutment structures are fitted coaxially over the threaded rod and secured to the rod inwardly of opposite ends of the rod. The abutment structures which the method and apparatus of the present invention are intended to be used with each comprise a circularly symmetric, hollow tubular body having an inner longitudinal portion consisting of a cylindrically-shaped tubular crown section, and an outer longitudinal portion consisting of a transversely disposed, circular flange section. The body of the abutment structure has a central coaxial bore of slightly larger diameter than the threaded rod to which a pair of abutment structures are fastened to assemble a self-sealing tie rod.
An apparatus for manufacturing self-sealing reinforcement tie rods according to the present invention includes a work plate having an upper surface in which is formed a shallow circular depression or cavity of the appropriate diameter to coaxially receive the outer flanged portion of an abutment structure, the depression having a lower flat support wall which supports the outer transverse wall surface of the flange. The support wall has formed therein a central coaxial pilot bore which has a diameter slightly larger than that of the threaded rod component of the self-sealing reinforcement tie rod. A base wall at the lower end of the pilot bore limits downward movement of the end of a tie rod inserted into the bore of the abutment structure to a predetermined extension distance of the tie rod below or outward of the outer transverse wall surface of the abutment structure flange.
The tie rod manufacturing apparatus according to the present invention includes at least a first pair of diametrically opposed ram punches having a radially inwardly directed line of action, each ram punch having at the inner end thereof a pair of vertically spaced apart chisel points which provide a pair of vertically aligned crimping surfaces which are driven radially inward by a ram actuator mechanism to a radial spacing slightly less than the diameter of the tie rod. Preferably, the apparatus includes a second pair of diametrically opposed ram punches similar to the first pair, but spaced circumferentially apart at a ninety-degree interval from the first pair of punches. The apparatus according to the present invention includes a pneumatic actuator cylinder which is coupled by lever arms to the ram punches, and a sensor for determining when a tie rod has been inserted a predetermined extension distance through an abutment structure, i.e., to the bottom of the pilot bore. The sensor produces an output signal which opens a solenoid that admits pressurized air to the actuator cylinder, causing a piston within the cylinder to produce an actuation force which drives the ram punches radially inward for a predetermined time interval.
A method for manufacturing self-sealing reinforcement tie rods according to the present invention includes the steps of placing the outer flange portion of a tubular abutment structure at a predetermined location on a work table plane, inserting a threaded tie rod through the central coaxial bore of the abutment structure to a predetermined extension distance therefrom, actuating at least a first pair of diametrically opposed, radially inwardly acting ram punches each having a pair of radially inwardly protruding tips which each indent both a portion of the tubular crown portion of the abutment structure and an underlying portion of the threaded rod, thereby causing cold-flow of a portion of the inner longitudinal wall of the crown into locking engagement with indentations formed in the tie rod, and then retracting the ram punches.